1. Field of the Invention
The present invention relates to an optical transmission apparatus configured to suppress or inhibit the occurrence of a light surge.
2. Description of the Related Art
Among conventional schemes for suppressing a light surge which gives rise to a problem in the use of an optical amplifier is an optical amplifier configuration disclosed, for example, in Document 1 mentioned below. The optical amplifier disclosed in Document 1 includes a detecting part for detecting the electric power of input light, a comparison part for comparing the value of the electric power of the input light with a predetermined value, and an output control part for controlling the gain or output of the optical amplifier. When the power of the input light is smaller than the predetermined value, the output control part reduces the gain or output of the optical amplifier, thereby keeping the peak value of a light surge small, which light surge may occur when the power of input light falls and then abruptly rises.
Another proposal to suppress the light surge is, for example, a light surge suppressing circuit disclosed in Document 2 mentioned below. This light surge suppressing circuit comprises a light surge compressing circuit for compressing a light surge contained in an input signal light output from an optical amplifier, and an optical output compensating circuit which during the occurrence of a sharp drop in the level of the input signal light, superimposes a pseudo signal on the input signal light to thereby make apparent compensation for the drop in the level of the input signal light. The light surge suppressing circuit is intended to prevent the occurrence of light surge and compensate for a steep drop in the input signal light level.
[Document 1] Japanese Patent No. 2696064 (paragraphs 0023, 0025, FIG. 1)
[Document 2] Japanese Patent Application Laid-Open No. 11-205238 (Summary, Means for Solving the Problem, FIG. 1)
For example, in patent document 1, since there is substantially no transmission line length between the detecting part for detecting the power of the input light and the optical amplifier, an excitation light source incorporated in the optical amplifier needs to be controlled within a very short time after the detection of a light surge, and hence no complex control is required to achieve a very high response speed therefor.
In patent document 2, there are inserted optical devices for suppressing light surge in optical transmission lines in the light surge compressing circuit and the optical output level compensating circuit, so that during normal operation their insertion losses deteriorates the quality of the optical transmission line, making it impossible to achieve high optical transmission performance. Further, since the light surge occurs in a stage preceding a light surge suppressing stage, there is a high possibility of the devices being broken down by the light surge.